The present invention generally relates to bone implants, such as dental implants. More particularly, the present invention is directed to a self-osteotomizing and self-grafting bone implant which creates its own osteotomy and facilitates bone growth and integration of the implant.
Traditionally, orthopedic medicine and dentistry have copied older established industries, like carpenters, to create fasteners for prosthetic items to be attached directly to bone in the form of various cone screws. In such non-medical, inanimate industries, as in cases of wood, plastic or metal, the principal of direct fasteners is based upon compressibility (wood), flexibility (plastic) or malleability (metal) or a combination of these properties being fastened to.
In all these cases, a hole is created in the receiving material slightly smaller than the selected screw or fastener for the job. The material shavings from these drillings have no cohesive or adhesive properties and are removed from the drilling site by the spiral action of the drill and discarded. The mass of the material that is removed by the drill is replaced mainly by the body of the screw or fastener.
The threads of the fastener take advantage of the three properties of compressibility, flexibility and malleability of the receiving material to engage it with large enough frictional force so as to secure the fastener to the recipient material. The ultimate tightness or securement of the fastener in non-vital objects is the same initial tightness that is achieved by the frictional forces between the body of the screw and the walls of the hole and engagement of the threads into the material. Such non-vital structures (wood, plastic, metal) are usually homogonous in nature with predictable compressibility, flexibility or malleability factors and therefore the strength and behavior of the fastener can be controlled by the various properties of the fastener body and threads.
Human bones, however, have different properties depending on their location. Each bone has different properties from outside to inside. Hip bone, spines and upper jaw are porous, whereas the lower jaw, cranium and long bones are impervious at the outer shell. They all have spongy and softer structure as their core is approached. This diverse structure of the bones from one part of the body to another and within the same area from cortex (outer layer) to medulla (inner layer), makes the bone an unpredictable material for implants and fasteners. Inconsistencies in vital bone structure have resulted in many limitations in the current procedures. This has resulted in medical professionals and medical device engineers establishing over engineering and rescuing techniques, such as placing more implants or fasteners than needed or using fasteners or implants which are wider or longer than necessary, to make their procedures as successful as possible.
Although human bones have no sensory innervations, the bones experience pain by the stretch receptors in the periosteom, the outer thin covering of the bone. Therefore, while the drilling of the bone does not contribute to post-operative pain, placement of current bone screws or implants that rely on frictional forces for their stability cause expansion of the recipient bone, resulting in the main source of post-operative pain in orthopedic and dental implant surgeries.
The limitations and unpredictable bone qualities are many times greater in dental implant surgery as the implants are placed in place of freshly extracted teeth or teeth that were previously lost, such as due to chronic infections that created voids in the bone. In current dental implant systems, the relative condensability of the bone is taken advantage of for initial implant stability. For implants supporting dental restorations, a hole is made in the bone (an osteotomy), which is slightly smaller in diameter than that of the proposed implant, by drilling at 800-1500 rotations per minute (RPM), typically with the use of saline coolant. The process usually involves creating progressively larger diameter holes which are drilled into the jawbone. Special twist drills are used in increasing the diameter until a hole of a size of 0.2-0.4 mm smaller than the implant cylinder or body is achieved.
The implant is then either tapped into this hole or more commonly “screwed” into the hole, much like a screw is driven into wood. Depending on the density of the recipient bone and the implant system in use, the osteotomy (hole) may be tapped before implant placement or the implants come with self-tapping features. In all these cases, the space for the implant is created mostly by drilling the native bone out and the implant is initially stabilized by condensing the immediate adjacent bone due to the implant being slightly larger than the tapped hole or osteotomy.
Creating a perfectly sized and shaped osteotomy is the greatest challenge for the implant dentist. Taking into consideration the fact that this osteotomy is performed in a physically unpredictable bone mass in the oral cavity between tongue and cheek, in a wet and bloody field with potential operator hand movement and patient movement creates many challenges for successful implant placement. Physically, jawbone in a live person varies greatly and unpredictably in density, condensability, texture and hardness from one site to another and at the same site from one mm in diameter or depth spot to the next. Live human bone is erratically fragile in small thicknesses. This fragility particularly complicates osteotomy creation in multi-rooted teeth sockets where thin webs of bone are the only anatomically correct position for the implant. All of these factors further depend on the condition and time of the extracted tooth and age of the implant recipient.
In current systems, the sequential drilling protocol removes and brings to surface any native bone that has occupied the space of the future implant. The bone shavings are often suctioned away along with the coolant liquid. Although there are commercially available “bone traps” that can be used to trap these shavings by the surgical suction mechanism, there are concerns with harvesting the bone in this manner due to potential bacterial contamination. Moreover, due to the nature of the suction mechanism, the trapped bone is repeatedly and cyclically washed and dried in the trap before it is recovered, thereby compromising the vitality and viability of the removed bone.
It can take a period of approximately three to six months after the emplacement of the body portion of the implant within the osteotomy for bone tissue to grow into the surface irregularities of the implant and secure the body portion of the implant in place within the bone bore or osteotomy. Following this three- to six-month period, an artificial tooth or other prosthetic component is typically secured to the implanted body portion, such as attaching a dental abutment to the implant. The most common cause of implant failure is the lack of initial stability, which is nothing but the inability and limitations of the system to create the perfectly sized and shaped osteotomy for the chosen implant and patient. It is important to know that the perfect size of the osteotomy for each implant size varies and depends on the condensability of the bone in that site, which can only be accurately known while the implant is being seated in the osteotomy. Inappropriate osteotomy size for a particular site is the most common cause of implant waste at dental offices that contributes to unnecessary higher cost to the consumers.
If the osteotomy size was overestimated, the primary stability suffers with risk of early mobility and implant loss in one to two weeks. If the size was underestimated, the primary stability will be excellent, but the excessive pressure at the implant bone interface, either through ischemic necrosis of the bone layer adjacent to the implant or through enzymatic activity from the pressure, causes the implant to fail in three to four weeks.
Another reason for bone necrosis and subsequent failure of dental implants is damaging the osteotomy site by overheating it during drilling. An overused, worn drill in a hard bone can generate enough heat to damage the bone to the extent that the implant does not integrate. Most implant systems recommend frequent changing of the drill sets, and others recommend “single use” drill sets to ensure sharp cutting edges every time. Needless to say, either way, there is a high per-implant cost in drilling supplies associated with the current systems.
In places where the implant is placed in thin bones, like the septum of a multi-rooted tooth, the success of current implants is limited due to the high chance of fracture of this septum either by sequential drillings or by the pressure of the implant itself.
The success of osseointegration depends on microscopically close adaptation of the vital host bone to the implant surface. The immediately placed implant by virtue of the way that it has become to be in its final position, such as by rotation, although immobile by at least a tripod of tight areas, has gaps filled with blood in its bone-implant interface. Provided that the conditions are favorable, this implant is considered “oseo-integrated” when new bone cells grow into these gaps, totally obliterating any space between the host bone and the implant. This process takes approximately two to six months and hence the typical waiting period of three to six months following implant placements for integration. If part of the implant surface is in grafted bone, other than autogenous bone, the integration time is further extended because usually the grafted material has to first get resorbed and then host bone grows into its space. Any micro or macro movement of the implant surface during this period prevents formation of bone next to its surface and results in failure.
Accordingly, there is a continuing need for an improved bone implant which will consistently result in adequate and quick anchoring of the implant to the bone, and thus implant stability. The present invention fulfills these needs, and provides other related advantages.